The invention relates to an apparatus for the treatment of waste water.
Waste water in a body such as a lagoon or a tank is typically treated by mixing air into the waste water. This air supports biological processes which change the waste water so that it can be returned to a stream, lake or larger body. A variety of mechanical and other aeration devices are available and typically such devices are mounted at the edge of the tank or lagoon, form a part of the bottom or sides thereof, or are suspended from fixed beams or the like over the tank or lagoon.
Floating surface aerators which spray waste water into the air to absorb atmospheric oxygen are inefficient, and accelerate thermal losses in the winter which leads to biological process failures and creates icing and freezing problems leading to mechanical failures. Moreover, floating aerators cannot be used in deep basins because of poor bottom mixing in the tank or lagoon. High maintenance costs are usually required.
Submerged aeration devices conserve thermal energy, thereby enhancing cold weather operation. They are free from icing and more efficient with greater mechanical reliability than surface aerators.
However, one drawback of submerged aerators has been the need to drain the tank or pond for installation and maintenance.
Suggestions have been made for a submerged aeration device which mixes a gas with waste water and is supported beneath the surface of the body of that waste water by a floating platform providing sufficient buoyancy to support the aeration device. The use of a floating platform provides considerably greater flexibility in positioning the aeration device to achieve maximum efficiency and results than fixed devices.
However, several problems have been encountered in using floating platforms to suspend aeration devices. One of the problems is platform stability. The aeration device creates considerable water and air movement and may create violent bubbling beneath the work platform with the water and bubbles rising and shaking the platform. An unstable platform normally leads to a reduction in efficiency of the aeration device which is shaken with the platform.
The present invention relates to a unique apparatus including a floating work platform for supporting and suspending an aeration device or the like in a stable and satisfactory manner.
One type of aeration device which is particularly satisfactory with the present invention is the jet aerator. Such a device typically includes a plurality of nozzles through which waste water is pumped with air being mixed with the waste water within each nozzle.
According to one aspect of the present invention, a conduit is used to connect a source of pressurized gas above the surface of the body of the water to the aeration devices which are disposed below the surface of the body of the water. In order to stabilize the platform and to make sure that the conduit is not a source of hazard to those who work on the platform, the conduit extends through the base of the floating platform, preferably at the water level and preferably to a central opening through the platform. The conduit then connects to the aeration devices suspended by a cable or the like through the central opening. The conduit thus acts as an outrigger, providing stability and forming an integral structural part of the platform.
The use of mixing devices of this type and particularly the use of jet aerators produces considerable upward flow of the water and entrained gases. At least some of the gases will escape from the surface of the body. Since the devices are suspended beneath the work platform, it is inevitable that a considerable amount of the water and gas flow will impinge beneath the platform. In one respect this can be an advantage, since if the gases are trapped as small bubbles for at least a short time beneath the platform, their residence time in contact with the water increases and the amount of absorption increases as well. However, if large bubbles form beneath the platform, the air surface in contact with the water is too small to effectively increase residence time. Further, these large bubbles cause the platform to become unstable. It has been found that formation of such large bubbles can be avoided, and the platform at the same time will effectively trap the small bubbles, if the dimensions of the aerating device are related to the dimensions of the platform.
More particularly, the present invention finds particular utility with a jet aeration device comprising a plurality of nozzles extending radially outward from a manifold containing both pressurized gas and waste water which is pumped therein. The waste water flows in a radially outward direction through the nozzles and air is mixed with the waste water as it passes through the respective nozzles. With such a device, it has been found that if the distance between the outlets of the most separated nozzles is at least as great as the smallest dimension of the floating work platform in the horizontal plane, large bubbles will not form and the residence time will be advantageously increased.
The co-pending application of the present applicant, Ser. No. 863,587, filed Dec. 22, 1977, now U.S. Pat. No. 4,152,259, describes a method and apparatus of backflushing a system such as described in the present invention. In this backflushing technique the pump which forces waste water through the nozzles is turned off while the air pressure is continued. The air then flushes the waste water in a reverse direction through the pump or through a separate connection, removing debris and the like which interfere with effecient operation of the system. This backflushing technique, particularly when it is done through the pump, creates great upwelling of water and entrained bubbles which can violently shake the raft. However, this problem has been resolved in the present invention by providing a central opening in the base through which the upwelling waves can dissipate their energy to the surface. The central opening has a cross-sectional area at least as great as the pump inlet area. Further, the central opening provides a simple and convenient way to suspend the aeration device beneath the platform and retrieve the device for maintenance.
As described below, the present invention includes a number of additional aspects which make the system efficient, stable and desirable. The base is preferably closed on all sides and filled with a suitable foam to provide buoyancy. The submerged aeration device is preferably supported and stabilized by means of a plurality of vertically extending guide bars, e.g., four. An A-frame support is mounted on the platform and the aeration device suspended from this A-frame support by means of a cable and winch.
Other objects and purposes will be clear from the following detailed description of the drawings.